The present invention is directed to a novel crystalline anhydrous sodium salt of 5-chloro-3-(2-thenoyl)-2-oxindole-1-carboxamide having advantageous properties for pharmaceutical formulation as an analgesic or antiinflammatory agent.
Kadin, U.S. Pat. No. 4,556,672 has disclosed said 5-chloro-3-(2-thenoyl)-2-oxindole-1-carboxamide, of the formula ##STR1## (or a pharmaceutically acceptable salt) as an especially preferred compound for use as an analgesic or antiinflammatory agent. In that disclosure the sodium salt of the compound of the formula (I) was alternatively isolated as a hemihydrate or hydrate. The monohydrate was rendered anhydrous by further drying. We have now determined that several hydrates are formed, generally as mixtures having various morphologies (e.g., amorphous and needle shaped crystals). These various hydrated forms generally have flow and electrostatic properties which make formulation difficult. We have also determined that the anhydrous product obtained by simple drying at elevated temperature and/or reduced pressure is amorphous and hygroscopic. It was therefore highly desirable to find a crystalline form of the sodium salt which might overcome these difficulties.